View Full Version : CNC big problems

04-01-2017, 09:43 PM
Hi all I'm new here first post, I recently bought a 3 axis cnc machine on ebay its a desktop usb. I've been trying to use it to make panels but I can't :( So I have a few questions, 1) How do I make panels? I've been importing stl files into freemill but I dont understand any of the menus. 2) At what point are you supposed to change your cutting piece to go from cutting the panel to engraving the text? I planned to paint the surface of the panel then secure it down to the bed and then cut it out somehow change the cutting tool during the operation to an engraving tool how? what software I have GRBL controller and freemill also gsimple but no idea how layers work. Sorry I am such a noob at this I just excited to start making panels but annoyed because I cant find a tutorial for my cnc. One more thing my working area is 240x160x50mm but there are no sensors to tell the motor to stop so it runs into the side rails how do I tell it where to work? Thanks. Theres a pic of my cnc attached.

04-02-2017, 03:21 AM
CNC work is something that takes quite a while to get to grips with.
The best advice I can give you would firstly to learn to design with a good CAD package, there are several free ones available (DesignSpark Mechanical for example).
Next find a CAM program that you can use to produce gcode from DXF files exported from your CAD program (I use Cam Bam, again there is a free version I believe).
With the gcode you produce I would suggest you use Mach3 to drive your CNC machine which runs the gcode.

As you can see, there is a lot to learn and those that produce panels have spent a lot of time to get there finished products.
Using a CNC milling machine is not as easy as using a 3D printer.

Great advice and information can be found on the Cnczone website and a quick search there came up with this link which may help you some http://www.cnczone.com/forums/deskcnc-controller-board/48481-cnc.html .

Don't take this as a negative response, just advice to help you get the most out of your new machine but there is a steep learning curve.

With regards to machine travel, you need to fit some limit switches to each axis, for my small router i used these http://www.ebay.co.uk/itm/SN04-N-Inductive-Proximity-Sensor-Detection-Switch-10-30V-Proximity-Switch-/322440745483?hash=item4b12f7520b:g:tcIAAOSwtfhYsAnL


04-02-2017, 12:48 PM
Thanks for the reply john really appreciate the feedback I'll look into the software you recommended. Your right about it not being as easy as 3D printing I've been 3 printing for a while now and its child's play compared to CNC :/ Thanks again.

04-02-2017, 09:49 PM
First things first. If you have a couple dollars and the controller supports them, get some limit, home, and e-stop switches, they are cheap and might save you big $$ in damage to your machine.
I found there were 2 difficult things in using the CNC: 1-CAD in general, 2-tool paths.
In addition:
Learn about machining plastic, so seek out some info on spiral, up-cut bits. The idea is to cut the plastic, eject the chips and keep the plastic from melting. the up-cut pulls the plastic chips out of the toolpath, along with the heat it absorbed during the cut.
Keep the bit-speed low, I use a cheap speed controller from Harbor Freight, and the feed-rate marginal.
I use 1/16" and 1/8" bits from Onsrud. They are expensive and brittle. Plenty of places have decent steel bits much cheaper. Making several more-shallow passes to get through the work is much better than rushing and breaking bits/ruining work.
If your machine supports G-code (almost ALL do), what's the software used to read the g-code into the controller? I use Mach and LinuxCNC. For CAD I use BobCAD. Try drawing a circle or square, and then generate G-code (toolpath) to send the machine. Try it without lowering the Z into material until you think it's correct. The general approach to making a panel is to cut the panel, leave the bulk material on the machine as a jig, remove the panel, paint it, let it dry, then put it back into the machine and do your engraving. Use a V-shaped bit for the engraving, you don't have to go too deep to get decent letters and lines.
I'm by far not the expert on this, but I learned every lesson the hard way. I bought my CNC machine just for making panels and it worked great. Later I got a laser cutter and prefer it to the CNC for most things I do. The advice on CNCZone is dead-on, a great place to get info, so is Sawmill Creek forums, for that matter, Gwen's forum here too. I will be glad to try and answer any questions you have, don't hesitate to seek additional input if my answers don't sound right!

04-03-2017, 08:42 AM
Did some more investigating. GRBL does have inputs that can be used for home/limits. I always prefer to use the inputs for limit, rather than home on machines, that don't have both, and in fact sometimes people position switches for both home and limit on the same input. You can drive the machine home manually until it hits the switches, move off just enough to clear the home switches, manually set this as the home position, and then have fail-safe limits on both ends of each axis. Also, I did find configuration settings in the software for setting soft limits on the machine. Is your Freemill integrated as a plugin to another CAD package? Did your controller come pre-programmed with this CNC machine, and was there a set of instructions for machine setup? We can double check all of the settings to make sure the stepper configuration and all of that is correct. Having the steps per pulse, etc. will cause endless problems. I can surely help you with all of this, be patient and we will get it going. Send me a link to where you bought the machine and I will hunt down specific info if you don't have it.